The present invention relates to the production of slaked lime.
Slaked lime, ie. an aqueous suspension of calcium hydroxide, is used in a variety of industrial applications. For example, a common use is in the production of precipitated calcium carbonate (pcc) by reaction with carbon dioxide.
Slaked lime is formed by reacting quicklime or calcium oxide with water. The quicklime is usually produced by thermally decomposing calcium carbonate, eg. obtained from a mineral source, such as limestone, in a furnace. Conventionally, the quicklime is obtained as a solid residue in the furnace. After cooling, the quicklime is usually handled dry, eg. packaged in bags or in bulk quantities which are stored and subsequently transported to a user. Alternatively, it may be conveyed dry directly to a user. Handling, storage and transport of dry quicklime produced in this conventional way presents problems because the quicklime is a hazardous alkaline material. Care has to be exercised to avoid accidental contact of the dry quicklime powder with water which affects properties of the product, eg. pcc, subsequently produced by use of the slaked lime obtained from the quicklime.
For pcc production, slaked lime is conventionally produced by mixing the quicklime with water in a vessel containing the water. If care is not taken when slaking conventionally produced quicklime, slaked lime produced in this way may be viscous even at relatively low solids levels and may contain grit arising from uncalcined calcium carbonate or from unreacted and water burned quicklime.